1BASICS_DENSITY = {
  2    'Concrete': 2500,
  3    'Brick': 2000,
  4    'Stone': 1600,
  5    'Wood': 600,
  6    'Steel': 7700
  7}
  8
  9class Material:
 10    _DENSITY = 1
 11
 12    def __init__(self, mass):
 13        self.mass = mass
 14        self.is_used = False
 15
 16    @property
 17    def volume(self):
 18        return self.mass / self._DENSITY
 19
 20
 21class Concrete(Material):
 22    _DENSITY = BASICS_DENSITY['Concrete']
 23
 24
 25class Brick(Material):
 26    _DENSITY = BASICS_DENSITY['Brick']
 27
 28
 29class Stone(Material):
 30    _DENSITY = BASICS_DENSITY['Stone']
 31
 32
 33class Wood(Material):
 34    _DENSITY = BASICS_DENSITY['Wood']
 35
 36
 37class Steel(Material):
 38    _DENSITY = BASICS_DENSITY['Steel']
 39
 40
 41class Factory:
 42    """Create different building materials including some interesting 'alloys'.
 43    A fancy way to demonstrate the factory design pattern"""
 44
 45    _valid_classes = {
 46        'Concrete': Concrete,
 47        'Brick': Brick,
 48        'Stone': Stone,
 49        'Wood': Wood,
 50        'Steel': Steel
 51    }  # we start with the basic classes first and gradually add dynamic ones
 52
 53    _all_produced_materials = []
 54
 55    def __init__(self):
 56        self._produced_materials = []
 57
 58    def _handle_kwargs(self, **kwargs):
 59        materials_list = []
 60        for material_name, mass in kwargs.items():
 61            if material_name not in self._valid_classes:
 62                raise ValueError('Invalid class name!')
 63            materials_list.append(self._valid_classes[material_name](mass))
 64        self._produced_materials.extend(materials_list)
 65        self._all_produced_materials.extend(materials_list)
 66        return tuple(materials_list)
 67
 68    @staticmethod
 69    def _create_new_class(class_name, density):
 70        new_class = type(class_name, (Material,), { '_DENSITY': density })
 71        return new_class
 72
 73    def _handle_args(self, *args):
 74        total_mass = 0
 75        all_names = []
 76
 77        for arg in args:
 78            if arg.is_used:
 79                raise AssertionError('This material is already used in some factory!')
 80            arg_class_name = type(arg).__name__
 81            total_mass += arg.mass
 82            split_names = arg_class_name.split('_')
 83            all_names.extend(split_names)
 84
 85        for arg in args:  # in another loop to make sure no fails happen when we mix used and unused args
 86            arg.is_used = True
 87
 88        all_names = sorted(all_names)
 89        combined_name = '_'.join(all_names)
 90
 91        if combined_name not in self._valid_classes:
 92            avg_density = sum(BASICS_DENSITY[name] for name in all_names) / len(all_names)
 93            self._valid_classes[combined_name] = self._create_new_class(combined_name, avg_density)
 94
 95        to_return = self._valid_classes[combined_name](total_mass)
 96
 97        self._produced_materials.append(to_return)
 98        self._all_produced_materials.append(to_return)
 99
100        return to_return
101
102    def __call__(self, *args, **kwargs):
103        if (not args and not kwargs) or (args and kwargs):
104            raise ValueError('Invalid arguments!')
105        if kwargs:
106            return self._handle_kwargs(**kwargs)
107        elif args:
108            return self._handle_args(*args)
109
110    def can_build(self, target_volume):
111        total_volume = sum(material.volume for material in self._produced_materials if not material.is_used)
112        return total_volume >= target_volume
113
114    @classmethod
115    def can_build_together(cls, target_volume):
116        total_volume = sum(material.volume for material in cls._all_produced_materials if not material.is_used)
117        return total_volume >= target_volume